1. Field of the Invention
The present invention relates to a liquid crystal display device used for a personal computer, a work station or the like and in particular to a technology effectively applied to a direct backlight unit used for the liquid crystal display device.
2. Description of the Related Art
A liquid crystal display module of a super twisted nematic type (hereinafter referred to as STN type) or a thin film transistor type (hereinafter referred to as TFT type) is widely used as a display device for a notebook personal computer and the like.
This liquid crystal display module is formed of a liquid crystal display panel having drain drivers and gate drivers arranged at the periphery and a backlight unit for applying light to the liquid crystal display panel.
This backlight unit is broadly classified into a side backlight unit and a direct backlight unit.
In the case of the liquid crystal display module used for a display device of a liquid crystal display module of a notebook personal computer, a side backlight is generally employed.
In recent years, the liquid crystal display module has been enlarged in size or in screen and has been used as a display device of a monitor. For the liquid crystal display module for such a large size or large screen monitor, a direct backlight unit is suitable because it can produce high luminance.
In this connection, the liquid crystal display module employing the direct backlight unit is disclosed, for example, in Japanese Unexamined Patent Publication No. 5-257141.
The direct backlight unit has a plurality of light sources (cold cathode fluorescent lamps), an optical member including a diffusion plate which light emitted from the plurality of light sources enters, and a reflector having a reflecting surface for reflecting light, radiated from the plurality of light sources to the side opposite to a liquid crystal display panel, to the side of the liquid crystal display panel.
On the other hand, in recent years, in a liquid crystal display module for a large screen monitor, the need for reducing thickness and picture frame width is increasing, as is the case with the liquid crystal display module for a notebook personal computer.
However, if the direct backlight unit is reduced in thickness, that is, the distance between the optical member and the reflector is reduced so as to reduce the thickness of the liquid crystal display module for a large screen monitor, of the light emitted from the respective light sources, the amount of light entering the region between the respective light sources of the optical member is decreased.
For this reason, there is presented the problem that the luminance in the region between the respective light sources on the surface of the liquid crystal display panel decreases as compared with the luminance in the region right above the respective light sources on the surface of the liquid crystal display panel to cause an unevenness in the luminance on the display surface of the liquid crystal display panel.
In order to solve the above problem and to make the luminance on the display surface of the liquid crystal display panel uniform, it is necessary to use a light curtain (for example, printing a dotted pattern on the diffusion panel of the optical member). However, since the light curtain makes the luminance uniform by reducing peak luminance, it has a drawback of reducing the luminance.
Further, the light curtain also has a drawback incapable of making the luminance sufficiently uniform because of variations in manufacture such as variations in accuracy in the alignment of the respective light sources and the respective dotted patterns constituting the light curtain.
The invention has been made to solve the above problems of the conventional technology. The object of the present invention is to provide a technology capable of reducing an unevenness in luminance caused on the display surface of a liquid crystal display element in a liquid crystal display device employing a direct backlight unit.
The above-mentioned object and the other objects and new features of the invention will be made clear by the description and the accompanying drawings of the specification.
Among the inventions disclosed in the present application, the outline of the typical inventions will be described in brief in the following.
That is, the invention is a liquid crystal display device having: a liquid crystal display element having two substrates opposed to each other and a liquid crystal layer sandwiched between the two substrates; a plurality of light sources disposed opposite to the display surface of the liquid crystal display element and radiating light to the liquid crystal display element; optical members interposed between the liquid crystal display element and the plurality of light sources; and a reflection member disposed opposite to the liquid crystal display element of the plurality of light sources, and is characterized in that the reflection member has, in the regions between the plurality of light sources, protrusions protruding to the plurality of light sources and arranged along the direction of extension of the plurality of light sources, and that the protrusion is triangular in cross section when it is cut by a plane perpendicular to the direction of extension of the plurality of light sources, and that assuming that the distance between the center portions of the plurality of light sources is L, the distance between the reflection member and the center portions of the plurality of light sources being d1, the height of the protrusion being h, and an angle formed by two sides of the protrusion protruding to the plurality of light sources being xcex8, these factors satisfies the following relations
hxe2x89xa7d1, tanxe2x88x921(2(h+d1))/Lxe2x89xa790xc2x0xe2x88x92xcex8.
In the preferable embodiment in accordance with the present invention, the above-mentioned protrusion has a cross section shaped like an isosceles triangle in which two sides of the protrusion protruding to the plurality of light sources are equal.
In the preferable embodiment in accordance with the invention, the above-mentioned protrusion has a cross section shaped like a triangle having a round corner at a vertex.
In the preferable embodiment in accordance with the invention, the vertex where the two sides of the protrusion protruding to the plurality of light sources cross each other is in the middle portion between the center portions of the plurality of light sources.
In the preferable embodiment in accordance with the invention, assuming that the distance between the reflection member and the optical member is D, the distance D satisfies the following relation
10 mm less than D less than 20 mm
In the preferable embodiment in accordance with the invention, the optical member includes a diffusion plate on which patterns for making luminance uniform are printed.
In the preferable embodiment in accordance with the invention, the above-mentioned protrusion has means for preventing deformation.
In the preferable embodiment in accordance with the invention, the means for preventing deformation are a plurality of thin plates disposed between two sides of the protrusion protruding to the plurality of light sources in the direction perpendicular to the direction of extension of the plurality of light sources.
In the preferable embodiment in accordance with the invention, the means for preventing deformation is a notch made at the vertex where two sides of the protrusion protruding to the plurality of light sources cross each other.
In the preferable embodiment in accordance with the invention, the reflection member is made of synthetic resin.
According to the means described above, the protrusions for reflection, each of which is triangular in cross section, are provided in the regions between the respective light sources of the reflection member in the direct backlight unit and effectively reflect light radiated from the respective light sources to the regions between the respective light sources of the optical member. Therefore, it is possible to reduce unevenness in luminance produced on the display surface of the liquid crystal display element as compared with the conventional liquid crystal display device.
Further, since the protrusion triangular in cross section is provided with the means for preventing deformation, it is possible to prevent the deformation of the reflection member and to enhance the strength thereof.